In the field of photovoltaic device manufacture, it has been long recognised that significant improvements in device efficiency are obtained if light can be internally reflected within the device such that its path length through the active region of the device is extended.
Techniques for extending the path length of light in the active region of the device are generally known as light trapping and usually involve texturing of the device surface.
In bulk material devices, the surface of the semiconductor material is directly textured by use of selective etching agents that etch certain crystal planes more rapidly than others, causing an angular or pyramidal surface profile.
It was generally thought that surface texturing would not be effective in thin film devices because traditional surface texturing is on a scale greater than film thickness of recent thin film devices, and because device film thicknesses are approaching the wavelength of light.
However, it has been found that surface texturing can be very effective in thin film devices provided that the scale of the texturing is less than the average film thickness but larger than the wavelength of light in the semiconductor material.
One effective method of achieving surface texturing on this scale is to texture the substrate before forming the semiconductor film in which the device is to be formed.
Texturing of the substrate can be by abrasion or etching but one effective method of texturing the substrate is by forming a textured film on the surface. The only effective methods previously identified for obtaining a uniform thin texture coating are spinning and chemical vapour deposition. These methods apply the textured film only to the surface of the substrate onto which the semiconductor layer will be deposited. It has always been considered that texturing the other surface of the substrate, which is to be exposed in use, would be detrimental to long term performance due to dust trapping and less effective cleaning when exposed to rain.
However, it has been found that with texturing of in the order of 1 μm or below, the problem of dirt accumulation is not sufficiently significant to present a performance problem.
Texturing the exposed surface also reduces specular reflection which enhances appearance, particularly if variations exist in glass flatness over the area of a panel (eg, up to 1 mz), or between adjacent panels. Reduced reflection also reduces glare, which could be an aviation hazard when large installations or large numbers of small installations are located in an area under a flight path.
a Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.b Any description of prior art documents herein is not an admission that the documents form part of the common general knowledge of the relevant art in Australia.c Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.